Question

4.1)

What three conditions must be satisfied in order to solve the critical section problem and why?

4.2)

Please answer each of the following questions briefly:

a)   What is deadlock avoidance? (2 points)

b)   What is deadlock prevention? (2 points)

c)   Please discuss a strategy for deadlock avoidance (3 points)

d)   Please discuss a strategy for deadlock prevention (3 points)

5. (Chapter 6) Please answer the following questions briefly (5 points each, total 10 points)

5.1)

Explain the process of starvation and how aging can be used to prevent it.

5.2)

What effect does the size of the time quantum have on the performance of an RR algorithm?

Refer to Operating System Concepts Essentials, 2nd Edition

Answer 1

4.1)The three conditions that are satisfied in order to solve critical section problem are:

  )Mutual Exclusion:if one process executes in critical section, no other process are allowed to execute in the critical section.

  )Progress:if no process is executing in the critical section and the other processes are waiting outside the critical section in order to enter the critical section ,then only those processes that are not execute the remainder critical section can participate that will enter the next.

  )Bounded Waiting:it implies that there exists a bound on the number of times a process is taken to enter  the critical section there after the process has made any request to enter the critical section and before the request is granted.

In order to synchronize the cooperative processes,we must do solving of critical section.we must solve the critical section problem in such a way by giving solution which satisfies the above three requirements.These are the three major requirements for synchronization mechanisms.   

4.2)

In Operating Systems,Deadlock is a process or a situation in where a set of processes are blocked because each process is holding a resource and it is waiting for another resource acquired by the other processes.

a)Deadlock avoidance:

  It is a process of avoiding deadlock,and it does not totally prevent deadlock.

  It ensures that system does not go in unsafe state.

In this Resource requests are done according to the available safe path.

  It requires the entire information about the existing resources,the available resources,and the resource requests.

  In this,request checks are automatically considered and it will check whether it is safe for the system or not.

b)Deadlock prevention:

It blocks at least one of the conditions which are necessary for the occurrence of deadlock.

In this all the resources are requested together.

It does not require any information about the existing resource,the available resources,and the resource requests.

It prevents deadlock by constraining request of resource and handling of resources.

  c)Deadlock avoidance strategy:

Must specify a maximum claim.

By knowing all future requests and releasing all the requests is a difficult process.

By estimating maximum demand for resources of each process is a easier procedure to produce.

In distributed Real Time Embedded Systems ,Deadlock occurs.

Thus a occurrence of deadlock avoidance also happens.

d)Deadlock prevention strategy:

For service oriented transaction processing an efficient deadlock prevention is needed.

  The reliability of business applications can be guaranteed by transaction processing.

In distribution management,locking resources are widely used to keep the system consistent.

It results in various deadlocks.

It will leads to deadlock prevention also.

5)

5.1)Starvation:

In operating system,like deadlock another problem also occurs. It is STARVATION.

It is a problem that occur in high priority processes which keep executing and low priority processes keeps blocked.

In this,resources are continuously utilized by high priority processes.

The priorities are assigned to the processes.

Starvation can be prevented by Aging.

Prevention of starvation by Aging:

Aging is a scheduling technique for preventing starvation.

In this,the gradually increasing of the priority processes that wait in the system for a long time.

In Aging,after some fixed amount of time quantum,the increasing of priority of low priority processes occurs.

By doing aging,as time passes,the lower priority process becomes higher priority process.

Thus we can allocate CPU for it.

5.2)Effect of size of the time quantum on performance of RR algorithm:

The scheduling of the process is one of the most important tasks on operating system.

Round Robin (RR) algorithm is one of the scheduling algorithm used by most of the operating systems.

In this,the ready processes are waiting in the ready queue,which seize the processor for a short period of time ,which is called as TIME QUANTUM.

If the time quantum is extremely large,The policy of the ROUND ROBIN (RR) algorithm is same as the policy of FIRST COME FIRST SERVE (FCFS) algorithm.

If the time quantum is extremely small,the approach behind RR algorithm which is called as process sharing,that leads in creating the appearance of each  n processor which has its own processor running at 1/n time the speed of real time processor.